References of "Vandewalle, Nicolas"
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See detailSuperparamagnetic colloids in viscous fluids
Darras, Alexis ULiege; Opsomer, Eric ULiege; Vandewalle, Nicolas ULiege et al

in Scientific Reports (2017), 7

The influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time for a few decades. However, the influence of important parameters, such as ... [more ▼]

The influence of a magnetic field on the aggregation process of superparamagnetic colloids has been well known on short time for a few decades. However, the influence of important parameters, such as viscosity of the liquid, has received only little attention. Moreover, the equilibrium state reached after a long time is still challenging on some aspects. Indeed, recent experimental measurements show deviations from pure analytical models in extreme conditions. Furthermore, current simulations would require several years of computing time to reach equilibrium state under those conditions. In the present paper, we show how viscosity influences the characteristic time of the aggregation process, with experimental measurements in agreement with previous theories on transient behaviour. Afterwards, we performed numerical simulations on equivalent systems with lower viscosities. Below a critical value of viscosity, a transition to a new aggregation regime is observed and analysed. We noticed this result can be used to reduce the numerical simulation time from several orders of magnitude, without modifying the intrinsic physical behaviour of the particles. However, it also implies that, for high magnetic fields, granular gases could have a very different behaviour from colloidal liquids. [less ▲]

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See detailVibration Induced Phenomena in Granular Media in Microgravity
Opsomer, Eric ULiege; Noirhomme, Martial ULiege; Vandewalle, Nicolas ULiege

in EPJ Web of Conferences (2017, June 30)

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See detailFrustrated crystallization of a monolayer of magnetized beads under geometrical confinement
Schockmel, Julien ULiege; Vandewalle, Nicolas ULiege; Opsomer, Eric ULiege et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2017)

We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short ... [more ▼]

We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short range magnetic dipole-dipole potential induced by an external magnetic field. The grains are confined by repulsing walls and are homogeneously distributed inside the cell. A two-dimensional (2d) Brownian motion is induced by horizontal mechanical vibrations. Therefore, the balance between magnetic interaction and agitation allows investigating 2d phases through direct visualization. The effect of both confinement size and shape on the grains’ organization in the low-energy state has been investigated. Concerning the confinement shape, triangular, square, pentagonal, hexagonal, heptagonal, and circular geometries have been considered. The grain organization was analyzed after a slow cooling process. Through the measurement of the averaged bond order parameter for the different confinement geometries, it has been shown that cell geometry strongly affects the ordering of the system. Moreover, many kinds of defects, whose observation rate is linked to the geometry, have been observed: disclinations, dislocations, defects chain, and also more exotic defects such as a rosette. Finally, the influence of confinement size has been investigated and we point out that no finite-size effect occurs for a hexagonal cell, but the finite-size effect changes from one geometry to another. [less ▲]

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See detailCoarsening dynamics of a granular lattice gas
Opsomer, Eric ULiege; Noirhomme, Martial ULiege; Ludewig, François et al

Poster (2017, March 23)

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See detailRealization of the Najafi-Golestanian microswimmer
Hubert, Maxime ULiege; Grosjean, Galien ULiege; Lagubeau, Guillaume et al

Conference (2017, March 14)

The development of artificial microswimmers, microscopic robots that swim in a fluid like sperm cells and motile bacteria, could cause a leap forward in various fields such as microfluidics, microsystems ... [more ▼]

The development of artificial microswimmers, microscopic robots that swim in a fluid like sperm cells and motile bacteria, could cause a leap forward in various fields such as microfluidics, microsystems, or minimally invasive medicine. Nature provides plenty of examples of efficient microswimmers. However, a bottom-up approach, looking at the simplest ingredients needed to generate a microswimmer, can lead to a deeper under- standing of the swimming problem. First described by Najafi and Golestanian 1 , a paradigmatic microswimmer is the three-linked-spheres model, which follows a minimalist approach for propulsion by shape shifting. In this presentation, we describe the experimental realisation of this microswimmer using self-assembled ferromagnetic particle at an air-water interface, powered by an uniform oscillating magnetic field 2 . A model, using two har- monic oscillators, reproduces the experimental findings. Because the model remains general, the same approach could be used to design a variety of efficient microswimmers. [less ▲]

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See detailSelf-assembled surface swimmers and micromanipulators
Grosjean, Galien ULiege; Hubert, Maxime ULiege; Lagubeau, Guillaume et al

Conference (2017, March)

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See detailSelf-assembled surface swimmers and micromanipulators
Grosjean, Galien ULiege; Hubert, Maxime ULiege; Lagubeau, Guillaume et al

Conference (2017, March)

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See detailRibbons of superparamagnetic colloids in magnetic field
Darras, Alexis ULiege; Fiscina, Jorge; Pakpour, Maryam et al

Conference (2017, March)

While the aggregation process of superparamagnetic colloids in strong magnetic eld is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a ... [more ▼]

While the aggregation process of superparamagnetic colloids in strong magnetic eld is well known on short time since a few decades, recent theoretical works predicted an equilibrium state reached after a long time. In this talk, we present experimental observations of this equilibrium state with a twodimensional system and we compare our data with the predictions of a pre-existing model. Above a critical aggregation size, a deviation between the model and the experimental data is observed. This deviation is explained by the formation of ribbon-shaped aggregates. The ribbons are formed due to lateral aggregation of chains. An estimation of the magnetic energy for chains and ribbons shows that ribbons are stable structures when the number of magnetic grains is higher than N=30. [less ▲]

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See detailCluster growth in driven granular gases
Noirhomme, Martial ULiege; Ludewig, François; Vandewalle, Nicolas ULiege et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2017)

We investigate numerically and theoretically the internal structures of a driven granular gas in cuboidal cell geometries. Clustering is reported and particles are classified as gaseous or clustered via a ... [more ▼]

We investigate numerically and theoretically the internal structures of a driven granular gas in cuboidal cell geometries. Clustering is reported and particles are classified as gaseous or clustered via a local packing fraction criterion based on a Voronoi tessellation. We observe that small clusters arise in the corners of the box, elucidating early reports of partial clustering. These aggregates have a condensation-like surface growth. When a critical size is reached, a structural transition occurs and all clusters merge together, leaving a hole in the center of the cell. This hole then becomes the new center of particle capture. Taking into account all structural modifications and defining a saturation packing fraction, we propose an empirical model for the cluster growth. [less ▲]

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See detailSegregation and pattern formation in dilute granular media under microgravity conditions
Opsomer, Eric ULiege; Noirhomme, Martial ULiege; Vandewalle, Nicolas ULiege et al

in NPJ Microgravity (2017), 3

Space exploration and exploitation face a major challenge: the handling of granular materials in low-gravity environments. Indeed, grains behave quite differently in space than on Earth, and the ... [more ▼]

Space exploration and exploitation face a major challenge: the handling of granular materials in low-gravity environments. Indeed, grains behave quite differently in space than on Earth, and the dissipative nature of the collisions between solid particles leads to clustering. Within poly-disperse materials, the question of segregation is highly relevant but has not been addressed so far in microgravity. From parabolic flight experiments on dilute binary granular media, we show that clustering can trigger a segregation mechanism, and we observe, for the first time, the formation of layered structures in the bulk. [less ▲]

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See detailMagnetocapillary self-assemblies: locomotion and micromanipulation along a liquid interface
Grosjean, Galien ULiege; Hubert, Maxime ULiege; Vandewalle, Nicolas ULiege

in Advances in Colloid and Interface Science (2017)

Review article on magnetocapillary self-assemblies, and in particular microswimmers, which includes new results concerning the manipulation of small objects and the mixing fluid at low Reynolds number.

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See detailRibbons of superparamagnetic colloids
Darras, Alexis ULiege; Fiscina, Jorge; Pakpour, Maryam et al

Poster (2016, October 12)

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See detailWalking droplets in confined geometries
Filoux, Boris ULiege; Hubert, Maxime ULiege; Schlagheck, Peter ULiege et al

Poster (2016, October 12)

When gently placing a droplet onto a vertically vibrated bath, under specific conditions, coalescence may be avoided. The drop bounces permanently. Upon increasing the forcing acceleration, the drop ... [more ▼]

When gently placing a droplet onto a vertically vibrated bath, under specific conditions, coalescence may be avoided. The drop bounces permanently. Upon increasing the forcing acceleration, the drop interacts with the wave it generates, and becomes a walker [1,2]. Recently, some 2D confining systems for walking droplets have been developed: cylindrical cavity, harmonic potential or the use of Coriolis force [3,4]. In addition, the interactions between two identical walkers have been studied in a 2D case [5]. Nevertheless, no study focuses on 1D dynamics and their properties. In this work, we show it is possible to confine a walker in a quasi mono-dimensional geometry by using a submerged annular cavity. We focus on the interactions between droplets, and show the interdistance quantization. Then, we study the speed of pairs of walkers and show that the distance between the drops affects the group speed: the closer the drops are, the faster they move. We also propose a numerical model to characterize the distance quantization, and the evolution of the speed of a string of droplets. Finally, we investigate the case of a string of droplets. We discuss the influence of the number of droplets and the distance between droplets on the string speed. 1. Y. Couder, S. Protière, E. Fort, and A. Boudaoud, Nature 437, 208 (2005).
 2. S. Protière, A. Boudaoud, and Y. Couder, J. Fluid Mech. 554, 85 (2006).
 3. S. Perrard, M. Labousse, M. Miskin, E. Fort, and Y. Couder, Nat. Commun. 5, 3219 (2014).
 4. M. Labousse and S. Perrard, Phys. Rev. E 90, 022913 (2014).
 5. C. Borghesi, J. Moukhtar, M. Labousse, A. Eddi, E. Fort, and Y. Couder, Phys. Rev. E 90, 063017 (2014). [less ▲]

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See detailNovel structures for optimal space partitions
Opsomer, Eric ULiege; Vandewalle, Nicolas ULiege

in New Journal of Physics (2016)

Partitioning space into polyhedra with a minimum total surface area is a fundamental question in science and mathematics. In 1887, Lord Kelvin conjectured that the optimal partition of space is obtained ... [more ▼]

Partitioning space into polyhedra with a minimum total surface area is a fundamental question in science and mathematics. In 1887, Lord Kelvin conjectured that the optimal partition of space is obtained with a 14-faced space-filling polyhedron, called tetrakaidecahedron. Kelvin’s conjecture resisted a century until Weaire and Phelan proposed in 1994 a new structure, made of eight polyhedra, obtained from numerical simulations. Herein, we propose a stochastic method for finding efficient polyhedral structures, maximizing the mean isoperimeter Q, instead of minimizing total area. We show that novel optimal structures emerge with non-equal cell volumes and uncurved facets. A partition made of 24 polyhedra, is found to surpass the previous known structures. Our work suggests that other structures with high isoperimeter values are still to be discovered in the pursuit of optimal space partitions. [less ▲]

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See detailRealization of the Najafi-Golestanian microswimmer
Grosjean, Galien ULiege; Hubert, Maxime ULiege; Lagubeau, Guillaume et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2016), 94(2), 021101

A paradigmatic microswimmer is the three-linked-spheres model, which follows a minimalist approach for propulsion by shape shifting. As such, it has been the subject of numerous analytical and numerical ... [more ▼]

A paradigmatic microswimmer is the three-linked-spheres model, which follows a minimalist approach for propulsion by shape shifting. As such, it has been the subject of numerous analytical and numerical studies. In this Rapid Communication, an experimental three-linked-spheres swimmer is created by self-assembling ferromagnetic particles at an air-water interface. It is powered by a uniform oscillating magnetic field. A model, using two harmonic oscillators, reproduces the experimental findings. Because the model remains general, the same approach could be used to design a variety of efficient microswimmers. [less ▲]

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See detailCoarsening dynamics of a granular lattice gas
Opsomer, Eric ULiege; Noirhomme, Martial ULiege; Ludewig, François et al

Poster (2016, July 22)

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See detailSelf-assembly of capillary multipoles
Poty, Martin ULiege; Lagubeau, Guillaume; Lumay, Geoffroy ULiege et al

Conference (2016, July 21)

Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced ... [more ▼]

Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, millimeter scale objets are produced. Their 3d shape is chosen in order to create capillary multipoles. The capillary interactions between these components can be either attractive or repulsive depending on the interface local deformations along the liquid-air interface. In order to understand how the shape of an object deforms the interface, we developed an original profilometry method. The measurements show that specific structures can be programmed by selecting the 3d branched shapes. [less ▲]

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